In the development of modern technology for wireless communication, for digital computing equipment, for portable consumer electronics, the requirements for high frequency, wide band and miniaturization are most critical and must be met. One of the modern trend in such development is centered on the use of embedded components in order to reduce real estate occupied by such circuits. For instance, it is desirable for a circuit designer to replace a most commonly used component of a capacitor in a surface mount technology with an embedded capacitor. This can be achieved by utilizing various structures or materials to fabricate the embedded capacitor. However, when various different fabrication methods are used to embed a capacitor, the connection between the embedded capacitor and other circuit components frequently produces parasitic effects, thus adversely affect the electrical characteristics of the capacitor. The parasitic effect becomes worse as the frequency of the capacitor becomes higher. In the worst case, the capacitor characteristics can be affected to such a stage that it exhibits the characteristics of electrical inductance. The threshold frequency for such transition in characteristics is known as the self-vibration frequency of the component. In modern digital or analog circuits, design of the circuit is more desirably high frequency and wide band. The characteristics of the component that function under high frequency becomes even more important. It is therefore highly desirable to improve the electrode connection method in an embedded capacitor in order to increase its self-vibration frequency for use in high frequency circuit applications.
Conventionally, as shown in U.S. Pat. No. 6,191,934 entitled “High Dielectric Constant Embedded Capacitors”, the connection method for the embedded capacitor is by edge connection. For instance, as shown in FIG. 1 of the patent, each electrode plate 14 is connected on the edge by a trace 16 wherein the terminal of the trace 16 is formed in a connecting pad 12. A series of connecting pads 12 are then electrically connected together by a lead 18 providing electrical connection for the embedded capacitor 10 to outside circuit components.
A disadvantage of the edge connection shown in FIG. 1 for the embedded capacitor 10 is that not only circuit real estate is increased due to the area occupied by trace 16 and by the connecting pads 12, the edge connection also produces unavoidable and difficult-to-analyze effective parasitic elements. As a result, the high frequency electrical characteristics of the embedded capacitor are severely affected to decrease the self-vibration frequency and to thus make such connection method inadequate in high frequency circuits.
In another conventional method for connecting embedded capacitors, as shown in FIG. 2A and by U.S. Pat. No. 5,400,210 entitled “Substrate Having a Built-In Capacitor and Process for Producing the Same”, through via 22 is utilized in an embedded capacitor 20 for connecting to the positive and negative electrode plates. The point of connection is far away from the geometric center of the electrode plate and thus causing unbalanced high frequency effective circuit due to the variation in the distances between the connection point and the edges of the electrode plates. Such unbalanced high frequency effective circuit further deteriorates the high frequency electrical characteristics of the embedded capacitor such as its self-vibration frequency.
In the recent development of microelectronic fabrication, the device dimensions are continuously being reduced. As a result, multi-layered microelectronic circuits are being designed and used. In the multi-layered microelectronic structures, embedded device elements are frequently used in order to achieve a high density packaging of the device. The ever-decreasing distances between the embedded elements lead to various undesirable parasitic effect produced in-between the embedded elements. Moreover, other elements that surround the embedded device such as wiring, capacitors and inductors further produce coupling effect due to the short distances in-between the elements. The coupling effect produces a loss in signal integrity due to cross-talking phenomenon.
It is therefore an object of the present invention to provide an embedded microelectronic capacitor without the drawbacks or shortcomings of the convention embedded capacitors.
It is another object of the present invention to provide an embedded microelectronic capacitor that incorporates ground shielding layers in the capacitor structure for maintaining signal integrity and reducing cross-talk.
It is a further object of the present invention to provide a method for fabricating an embedded capacitor that incorporates ground shielding layers.